Nitrobenzodifuroxan compounds, including their salts, and methods thereof

ABSTRACT

A nitrobenzodifuroxan compound having the chemical structure of: 
     
       
         
         
             
             
         
       
         
         
           
             wherein two of the R 1 , R 2 , R 3  and R 4  comprise oxygen or are absent, and only one of R 1  or R 2  is present, and only one of R 3  and R 4  is present, and wherein x is hydrolyzed or hydrolyzable. The salt of the hydroxynitrobenzodifuroxan of this compound is useful in explosive compositions.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention described herein may be manufactured and used by or forthe government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefore.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention provides nitrobenzodifuroxan compounds, such asmethoxynitrobenzodifuroxan and hydroxynitrobenzodifuroxan, and itssalts.

2. Brief Description of the Related Art

Toxicity and environmental concerns are present with the use of leadazide and lead styphnate, particularly when used in ordnance items suchas initiating materials in primary explosives. Replacement materials forlead azide and lead styphnate are optimal with high autoignitiontemperatures of at least 200° C. or higher.

In example 11 of U.S. Pat. No. 3,163,561 to Hardy et al.,trichlorotrinitrobenzene and sodium azide are used as reagents to makebenzotrifuroxan. In U.S. Pat. No. 5,149,818 to Christian et al., aninsensitive explosive material of aminonitrobenzodifuroxan is formed.However, neither of these patents disclose a formation of a sensitivenitrobenzodifuroxan explosive composition.

There is a need in the art to provide initiating materials employingnon-heavy metal primary explosives that are sensitive explosives withhigh autoignition temperatures. The present invention addresses this andother needs.

SUMMARY OF THE INVENTION

The present invention includes a nitrobenzodifuroxan compound having thechemical structure of:

wherein R₁, R₂, R₃ and R₄ comprise oxygen or are absent, for a total oftwo oxygen atoms, and only one of R₁ or R₂ is present, and only one ofR₃ and R₄ is present, and wherein x is a hydrolyzed or hydrolyzablesubstituent. Preferred compounds include methoxynitrobenzodifuroxan andhydroxynitrobenzodifuroxan.

The present invention also includes salts of hydroxynitrobenzodifuroxan,including Form A and Form B salts.

Additionally, the present invention includes a process for producinghydroxynitrobenzodifuroxan comprising the steps of providing ahydrolyzable nitrobenzodifuroxan and hydrolyzing the nitrobenzodifuroxaneffective to form hydroxynitrobenzodifuroxan, with a further step offorming the salt of the hydroxynitrobenzodifuroxan.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates Form A and Form B, hydroxynitrobenzodifuroxan,potassium salt of the present invention, with x-ray analysis of therespective structures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides novel hydrolyzable and hydrolyzednitrobenzodifuroxan materials, such as methoxynitrobenzodifuroxan andhydroxynitrobenzodifuroxan, including its salts, and methods ofproducing these materials. These nitrobenzodifuroxan compounds areuseful in explosive compositions. Hydroxynitrobenzodifuroxan materialsof the present invention include hydroxynitrobenzodifuroxan compoundsand their salts. Metal salts of hydroxynitrobenzodifuroxan areparticularly useful as sensitive explosives with high autoignitiontemperatures. The furoxan groups of the hydroxynitrobenzodifuroxanmaterials, in conjuction with the oxy-metal group, provide sensitivity.In addition, the oxy-metal group provides higher melting points andautoignition temperatures. As such, these hydroxynitrobenzodifuroxanmaterials are useful as lead azide and lead styphnate replacements inexplosive compositions.

The present invention includes a nitrobenzodifuroxan compound having thechemical structure of:

wherein R₁, R₂, R₃ and R₄ comprise oxygen or are absent, for a total oftwo oxygen atoms, and only one of R₁ or R₂ is present, and only one ofR₃ and R₄ is present, and wherein x is a hydrolyzed or hydrolyzablesubstituent. Representative examples of x include OH, OCH₃, Cl, F, Br,OR, OC(O)R, where R comprises an alkyl group having from about 1 toabout 3 carbon atoms, and other like units known to hydrolyze,combinations thereof, and other like substituents. Preferably, xcomprises an OH group forming the hydroxynitrobenzodifuroxan, or an OCH₃forming the methoxynitrobenzodifuroxan.

In a particularly preferred embodiment, the hydroxynitrobenzodifuroxanof the present invention comprises the hydroxynitrobenzodifuroxan salt.The hydroxynitrobenzodifuroxan salt is formed in Form A or Form B, asshown below.

Form A and Form B of the hydroxynitrobenzodifuroxan salt have thegeneral chemical structure, below. In the general structures, two of theR₁, R₂, R₃ and R₄ comprise an oxygen atom, two are absent, and only oneof R₁ or R₂ is present, and only one of R₃ and R₄ is present, and Z^(⊕)represents a cation.

The preferred chemical structures of Form A and Form B of a potassiumhydroxynitrobenzodifuroxan salt are shown below.

The hydroxynitrobenzodifuroxan salts of the present invention mayinclude any appropriate salt, such as alkaline metal salts, other metalsalts and amine salts. Representative alkaline metal salts includepotassium, sodium, rubidium, lithium, cesium, magnesium, calcium,strontium, barium, etc., and combinations thereof, and the like.Additionally, representative other metal salts of thehydroxynitrobenzodifuroxan include cobalt (Co), copper (Cu), aluminum(Al), nickel (Ni), iron (Fe), titanium (Ti), antimony (Sb), zinc (Zn),zirconium (Zr), etc., combinations thereof, and the like. Preferredhydroxynitrobenzodifuroxan salts include potassiumhydroxynitrobenzodifuroxan salts.

With acidic compounds, such as hydroxynitrobenzodifuroxan, other typesof salts may also be formed, such as amine salts. Amine salts may havealternative uses such as propellant burning rate modifiers.Representative amine salts of the hydroxynitrobenzodifuroxan includeH₂NC(NH₂)NHCONH₂, C(NHNH₂)₃, NH₂NH₃, NH₄, H₂NNHC(NH₂)NH₂,(H₂NNH)₂C(NH₂), C(NH₂)₃, (HONH₃), combinations thereof, and the like.Numerous heterocyclic amine salts of hydroxynitrobenzodifuroxan may alsobe formed and representative salts include salts from guanazole(3,5-diamino-1,2,4-triazole), 5-aminotetrazole,3,6-dihydrazino-1,2-4,5-tetrazine, etc.

As seen in FIG. 1, an x-ray analysis is illustrated for Form A and FormB, hydroxynitrobenzodifuroxan, potassium salt of the present invention.A merged superposition of the two different anions was seen in the x-rayanalysis, and each individual anion was mathematically extracted bymodeling the image as a sum of two parts. The drawing shows the twodifferent anion crystal structures ionically bonded to the potassiumcation.

The present invention further includes the process for producing ahydrolyzable nitrobenzodifuroxan, such as methoxynitrobenzodifuroxan,and further processing a hydroxynitrobenzodifuroxan, and its salt.Generally, the formation of the hydrolyzable nitrobenzodifuroxan of thepresent invention, represented in Formula I, preferably includes thereaction sequence of:

(a) a tri-substituted trinitrobenzene, such as di-substitutedtrinitroanisole, is treated to produce a substituteddiazidotrinitrobenzene (diazidotrinitroanisole); and,

(b) the substituted diazidotrinitrobenzene (diazidotrinitroanisole) istreated to produce a substituted nitrobenzodifuroxan(methoxynitrobenzodifuroxan).

Generally, the formation of hydroxynitrobenzodifuroxan (represented byFormula I, above, with x being OH), and its salts, of the presentinvention preferably includes the reaction sequence of:

(c) the substituted nitrobenzodifuroxan, formed above, is hydrolyzed toproduce hydroxynitrobenzodifuroxan; and,

(d) with the formation of the hydroxynitrobenzodifuroxan, an additionalstep of converting the hydroxynitrobenzodifuroxan to its salt, such asby neutralization or by ion exchange reactions, may be done.

In the first step of forming the hydroxynitrobenzodifuroxan compound,the tri-substituted trinitrobenzene, preferably a di-substitutedtrinitroanisole, is used. In addition to the three nitro substituents onthe benzo-structure, the trinitrobenzene includes two reactive sites forformation of N₃ substituents. Typical leaving groups at these tworeactive sites may include, for example without limitation, chlorine,fluorine, bromine, iodine, nitro, etc. and combinations thereof. Theseleaving groups are removed with the application of an appropriatereactant, including treatment with an azide, such as sodium azide,trimethylsilyl azide, and combinations thereof. Preferably, the leavinggroup includes chlorine. Treatment of the trinitrobenzene forms N₃substituents at the reactive sites to form the substituteddiazidotrinitrobenzene.

The substituted diazidotrinitrobenzene is further treated to produce anitrobenzodifuroxan, such as methoxynitrobenzodifuroxan,chloronitrobenzodifuroxan, fluoronitrobenzodifuroxan, etc, withmethoxynitrobenzodifuroxan preferred. Hydrolyzation of thisnitrobenzodifuroxan produces the hydroxynitrobenzodifuroxan.

Once formed, the hydroxynitrobenzodifuroxan may be further processed toform the hydroxynitrobenzodifuroxan salt. With the formation of thehydroxynitrobenzodifuroxan, an additional step of converting thehydroxynitrobenzodifuroxan to its salt, such as by neutralization or byion exchange reactions, may be done. Representative neutralizationreagents include metal hydroxides, metal oxides or amine bases,preferably with the aid of a solvent. Appropriate metal salts of weakacids, such as metal salts of acetic acid (potassium acetate, forexample), may also be used as neutralization reagents. Representativeion exchange reactions include metal ion exchange by precipitation fromsolvent or metal ion exchange using an ion exchange resin.

Referring to Scheme 1A, below, the general reaction sequence is shown(Y₁ and Y₂ represent leaving groups, Y_(x) represents a hydrolyzablesubstituent and Z^(⊕) represents a cation).

In a more specific embodiment of the general scheme (shown in Scheme 1A)for forming the hydroxynitrobenzodifuroxan, and its salts, of thepresent invention, formation is provided by the following reactionsequence (shown in Scheme 1B, below):

As seen in Scheme 1B, below, the reaction sequence includes:

(a) 3,5-dichloro-2,4,6-trinitroanisole is treated with sodium azide toproduce 3,5-diazido-2,4,6-trinitroanisole, as exemplified in Example 1;

(b) the 3,5-diazido-2,4,6-trinitroanisole is heated in an appropriatesolvent to produce methoxynitrobenzodifuroxan, as exemplified in Example2;

(c) the methoxynitrobenzodifuroxan is hydrolyzed to producehydroxynitrobenzodifuroxan, as exemplified in Example 3; and,

(d) hydroxynitrobenzodifuroxan is converted to salts by neutralization,as exemplified in Examples 4 and 5, or by ion exchange reactions.

EXAMPLE 1 Preparation of 3,5-diazido-2,4,6-trinitroanisole

A solution of 3,5-dichloro-2,4,6-trinitroanisole (1.50 g, 4.8 mmol) indimethyl carbonate (15 mL) was stirred in a 100 mL one-neckround-bottomed flask. A solution of tetrabutylammonium bromide in water(4.4 mL) was added. [The solution of tetrabutylammonium bromide wasprepared by dissolving it (0.30 g) in distilled water (30 mL) and using4.4 mL of this solution]. A solution of sodium azide (0.90 g, 13.8 mmol)in distilled water (18 mL) was then added. The flask was stoppered andthe mixture was stirred vigorously at room temp for 22 hr.

At this point, thin layer chromatography (TLC) was performed. TLC (usingtoluene/heptane 50/50 by volume as developer) of a small sample of thelower layer (diluted with acetone) indicated the reaction was complete(R_(F) of diazido-product and the starting material are 0.46 and 0.62,respectively; note that the diazido product turns yellow after standingon the TLC plate). The lower yellow layer was separated and the upperaqueous phase was extracted with dimethyl carbonate (3×5 mL). The yellowlayer and extracts were combined. TLC and ¹H NMR analyses indicated thedimethyl carbonate solution contained essentially pure3,5-diazido-2,4,6-trinitroanisole. ¹H NMR (acetone-d₆): 4.11 (s).

EXAMPLE 2 Preparation of Methoxynitrobenzodifuroxan

The volatiles from the combined dimethyl carbonate yellowlayer/extracts, from Example 1 above, were cautiously removed (withoutheating above room temperature) until the remaining volume of dimethylcarbonate was 10 mL. Toluene (40 mL) was added and the toluene/dimethylcarbonate solution was dried over anhydrous sodium sulfate overnight.The sodium sulfate was removed by filtration and the filter cake waswashed with toluene (3×7 mL). The filtrate was heated in an oil bathnear 100° C. for 7 hr. After 4.5 hr, TLC (toluene as developer) showed asmall amount of the starting diazido compound. (The R_(F) ofmethoxynitrobenzodifuroxan is about 0.64; the R_(F) of the startingdiazido compound is 0.77; the methoxynitrobenzodifuroxan product leavesa trail from the origin on the TLC plate, presumably due to hydrolysis.)

The reaction solution was allowed to cool to room temperature and standovernight before the solution was decanted from a small amount (0.03 g)of a dark precipitate. The volatiles were cautiously removed (withoutheating above room temperature) to give 1.39 g of residue (mostly solidwith some oil). The residue was stirred with chloroform (10 mL) at roomtemperature to give insoluble crystals. The mixture was cooled at 5° C.for 1 hr and then at −15° C. for 30 min before the crystals were removedand washed with cold (−15° C.) chloroform. The yellow-brown crystalsweighed 0.60 g, mp 149–152° C. A second crop gave an additional 0.11 g(mp 140–145° C.) of yellow-brown crystals. The yield of crystallinemethoxynitrobenzodifuroxan was about 55%. ¹H NMR (DMSO-d₆, contains someabsorbed H₂O): singlets (OCH₃) at 3.99, 4.19, 4.49 and 4.54 that vary inintensity over time; after 22 hr, only the peak at 3.99 remains; also apeak of increasing intensity at 3.18 (methanol) and broader peaksbetween 3.5 to 4.9 (H₂O/OH). These results indicate that themethoxynitrobenzodifuroxan is undergoing rearrangements (to form furoxanisomers) and also is undergoing hydrolysis. ¹H NMR (dry acetone-d₆):singlets (OCH₃) at 4.28, 4.59 and 4.63. IR (KBr): 1685, 1585, 1528,1352, 1297, 1087, 999, 769 cm⁻¹.

EXAMPLE 3 Preparation of Hydroxynitrobenzodifuroxan

Methoxynitrobenzodifuroxan (0.30 g, mp 149–152° C.), prepared as inExample 2 above, was dissolved by stirring in acetone (10 mL). Distilledwater (2 mL) was added. (Some product precipitated from solution whenthe water was added, but re-dissolved as the mixture was heated towards52–54° C.) The solution was held near 55° C. for 1.7 hr during whichtime it turned dark red brown. The volatiles were cautiously removed(without heating above room temperature) to give a red-brown solid (0.34g), which was then stirred in distilled water (5 mL) at roomtemperature. A very small amount (0.01 g) of insoluble yellow solid wasremoved by filtration and washed with of distilled water (2×1.5 mL). Thevolume of the filtrate was 8 mL. The water was removed from one mL ofthe filtrate (without heating above room temperature) to give a lightred solid, which had a melting point of 95° C. (with vigorousdecomposition).

EXAMPLE 4 Preparation of Hydroxynitrobenzodifuroxan, Potassium Salt

The remainder of the filtrate (7 mL) from Example 3 above was stirred atroom temperature while potassium carbonate (0.16 g) was slowly added inportions. Crystals precipitated as the solution was neutralized. Themixture was cooled to 5° C. and the deep red-brown crystals were removedand washed with ice-cold water (3×1.5 mL). The red-brown crystals wereair dried to give hydroxynitrobenzodifuroxan, potassium salt (0.18 g,63% yield based on methoxynitrobenzodifuroxan). The red-brown crystalsexplode in the vicinity of 200° C. ¹³C NMR (D₂O): 110.9, 140.1, 149.8,150.9 162.8, 163.0 (The D₂O solution was prepared at 60° C.; then cooledto room temperature without precipitation from solution). ¹³C NMR(DMSO-d₆): 97.2, 99.4, 101.8, 105.9, 110.0, 114.9, 116.4, 140.3, 150.1,151.0, 151.5, 159.3, 160.6, 161.7 [The numerous peaks in DMSO-d₆ arepresumably due to furoxan isomers that form in solution. Completeremoval of the DMSO-d₆ solvent under reduced pressure gave a red-browncrystalline residue that behaves as the original crystals (explodes inthe vicinity of 200° C.)]. IR (total attenuated reflectance): 1698,1648, 1574, 1549, 1460, 1359, 1337, 1277 (very strong), 1236, 1217,1081, 970, 938, 891, 800, 759 cm⁻¹.

Crystal structure analysis showed that the red-brown crystals containtwo forms, Form A and Form B, of the hydroxynitrobenzodifuroxan,potassium salt (shown in FIG. 1), in approximately equal amounts.Differential scanning calorimetry (DSC) showed the potassium salt tohave an autoignition temperature of approximately 200° C. (at a heatingrate of 20° C. per minute).

EXAMPLE 5 Preparation of Hydroxynitrobenzodifuroxan, Rubidium Salt

A solution containing hydroxynitrobenzodifuroxan (0.34 g) in water (8mL) was stirred at room temperature while aqueous rubidium hydroxidesolution was slowly added to raise the pH to 7 to 8 (by pH paper) andform a dark brown crystalline precipitate. [The aqueous rubidiumhydroxide solution was prepared by diluting 0.6 g of a 50 wt. % aqueoussolution of rubidium hydroxide with water (2 mL); about 1 mL of thediluted solution was required for the neutralization.] The mixture wascooled to 5° C. for 30 minutes before the crystals were removed andwashed with ice-cold water (3×1 mL). The first crop gave 0.11 g of darkred-brown crystals. Concentration of the filtrate gave a second crop(0.02 g), raising the total yield to 0.13 g (31%). The crystals explodein the vicinity of 200° C., in very similar manner to the potassiumsalt.

In a less preferred embodiment, the hydroxynitrobenzodifuroxan, and itssalts, of the present invention include formation provided by thereaction sequence using a trichlorotrinitrobenzene. This was difficultto control after substitution of the first two chlorine leaving groups,as the replacement of the third chlorine atom readily occurred oncereplacement of the first two chlorine atoms had occurred. As such, it isexpected that other reactants having identical substituents in the threelocations may experience similar control issues.

The present invention also addresses a need for thermally stable primaryinitiating explosives that are sensitive to laser initiation, i.e., aneed for primary explosives that will initiate by absorbinglaser-emitted light. As the hydroxynitrobenzodifuroxan, potassium salthas absorptions at 500 and 400 nm, the compound may be tailored tospecialized initiation procedures. This ability to absorb lightindicates that salts of hydroxynitrobenzodifuroxan are potentiallyuseful as laser sensitive initiating materials.

The foregoing summary, description, and examples of the presentinvention are not intended to be limiting, but are only exemplary of theinventive features that are defined in the claims.

1. A nitrobenzodifuroxan compound consisting of a chemical structure:

wherein two of R₁, R₂, R₃ and R₄ consist of oxygen, for a total of twooxygen atoms so that only one of R₁ and R₂ is present as said oxygen,and only one of R₃ and R₄ is present as said oxygen, and wherein x isone of a hydrolyzed substituent and a hydrolyzable substituent.
 2. Thecompound of claim 1, wherein x is selected from OH, Cl, F, Br, and OR,where R is an alkyl group consists of from about 1 to about 3 carbonatoms.
 3. The compound of claim 1, wherein x is selected from OH andOCH₃.
 4. The compound of claim 3, wherein said nitrobenzodifuroxancompound is a methoxynitrobenzodifuroxan compound.
 5. The compound ofclaim 1, wherein said nitrobenzodifuroxan compound is ahydroxynitrobenzodifuroxan compound.
 6. A hydroxynitrobenzodifuroxancompound, including a salt thereof, consisting of a chemical structure:

wherein two of R₁, R₂, R₃ and R₄ consist of oxygen for a total of twooxygen atoms so that only one of R₁ and R₂ is present as said oxygen,and only one of R₃ and R₄ is present as said oxygen and wherein x is anOH substituent.
 7. The hydroxynitrobenzodifuroxan compound of claim 6,consisting of a salt of hydroxynitrobenzodifuroxan compound.
 8. Thehydroxynitrobenzodifuroxan compound of claim 7, consisting of Form A ofhydroxynitrobenzodifuroxan salt.
 9. The hydroxynitrobenzodifuroxan ofclaim 7, consisting of Form B of hydroxynitrobenzodifuroxan salt. 10.The hydroxynitrobenzodifuroxan compound of claim 7, wherein the salt ofsaid hydroxynitrobenzodifuroxan compound is selected from alkaline metalsalts, other metal salts and amine salts.
 11. Thehydroxynitrobenzodifuroxan compound of claim 7, wherein said salt ofsaid hydroxynitrobenzodifuroxan compound is an alkaline metal saltselected from at least one of potassium, sodium, rubidium, lithium,cesium, magnesium, calcium, strontium, and barium.
 12. Thehydroxynitrobenzodifuroxan compound of claim 7, wherein said salt ofsaid hydroxynitrobenzodifuroxan compound is an amine salt selected fromat least one of H₂NC(NH₂)NHCONH₂, C(NHNH₂)₃, NH₂NH₃, NH₄,H₂NNHC(NH₂)NH₂, (H₂NNH)₂C(NH₂), C(NH₂)₃, and (HONH₃).
 13. Thehydroxynitrobenzodifuroxan compound of claim 7, wherein said salt ofsaid hydroxynitrobenzodifuroxan compound is a metal salt selected fromat least one of cobalt (Co), copper (Cu), aluminum (Al), nickel (Ni),iron (Fe), titanium (Ti), antimony (Sb), zinc (Zn), and zirconium (Zr).